In a known drive device and method for a three-phase brushless motor, sensorless control is performed using six energization modes each for selecting two phases to be energized from the three phases of the three-phase brushless motor. Specifically, the sensorless control is performed by sequentially switching between these six energization modes based on comparison results between a reference voltage and a pulse induced voltage (induced voltage) that is generated in a non-energized phase (open-circuit phase) and that varies depending on the angular position of the rotor. In such drive device and method, the angular position (initial position) of the magnetic pole of the rotor from which the rotor that has stopped starts to rotate in a predetermined direction is estimated (see Patent Document 1, for example).
Specifically, in such drive device and method for a brushless motor, the initial position of the rotor is estimated as follows. First, the brushless motor is energized according to the six energization modes, and detects voltages each induced in a non-energized phase by energization according to the corresponding energization mode. Then, the sum and difference of the pulse induced voltages in each two energization modes that share a non-energized phase are calculated. Finally, the initial position of the rotor is estimated based on the size comparison between the three induced voltage sums calculated as above as well as on the size comparison between the three induced voltage differences calculated as above.